The present invention relates to an X-ray apparatus and more particularly relates to techniques which can effectively be applied to exposure control for controlling properly or pertinently the conditions for generating X-rays in a fluoroscopy as well as in a radiography for X-ray diagnosis.
In the conventional X-ray fluoroscopy/radiography system, the automatic X-ray exposure apparatus is so designed as to pick up a portion of output light of an X-ray image intensifier or X-ray I.I. for detection by means of a photomultiplier or the like to thereby effect X-ray fluoroscopy and radiography controls on the basis of the detection signal. By way of example, for the X-ray fluoroscopy control, a feedback control is performed for a tube current and a tube voltage of an X-ray tube or aperture of an optical stop or iris so that an integral value of the detection signal outputted from the photomultiplier per unit time can assume a constant value, whereby brightness of the X-ray fluoroscopic image is constantly held at a pertinent level or value. Further, in the X-ray radiography control, X-rays are interrupted at a time point when the integral value of the detection signal outputted from the photomultiplier has attained a predetermined value, to thereby render available the X-ray radiographic image of proper brightness (phototimer).
As another example of the automatic X-ray exposure control method, there can be mentioned an automatic X-ray exposure apparatus described in Japanese Patent laid-open Publication JP-A-57-88698. In this automatic X-ray exposure apparatus, a plurality of photodiodes are employed for detecting output light of the X-ray I.I. in place of the photomultiplier mentioned above, wherein the X-ray fluoroscopy and radiography control is carried out on the basis of outputs of several photodiodes selected from the plural photodiodes.
In the automatic X-ray exposure control apparatus in which the photomultiplier is employed, as described above, a portion of the output light of the X-ray I.I. is picked up by the photomultiplier by way of a half mirror. Consequently, the amount of light inputted to a television camera will decrease, giving rise to a problem that light utilization efficiency is degraded. Besides, because the light pick-up field is disposed at only one location in the vicinity of the X-ray I.I., difficulty is encountered in effecting the control so that the image having proper or desirable brightness as a whole can be ensured for the X-ray images exhibiting various X-ray absorption dose distributions.
On the other hand, in the automatic X-ray exposure control apparatus described in Japanese Patent laid-open Publication JP-A-57-88698, the light pick-up field can be enlarged by disposing a plurality of photodiodes in place of the photomultiplier. However, the number of photodiodes is ordinarily in a range of eight to twelve or so. Consequently, in the case where one or more photodiodes are positioned near to a boundary between the X-rays transmitted through an object under inspection and the directly incident X-rays, a slight movement of the object under inspection will bring about significant variation in the amount of X-rays impinging onto these photodiodes, incurring a problem that the tone of the displayed image undergo remarkable variation.
As a method of coping with the problems described above, there has been proposed a method of performing the X-ray fluoroscopy/radiography control for an object under inspection by using directly a video signal outputted from a television camera.
However, this method suffers problems described below and thus encounters difficulty in realization for practical applications.
By way of example, because the dynamic range of the television camera is very narrow when compared with that of the photomultiplier and the photodiode array, halation will take place as the amount of light increases, making it impossible to detect accurately the X-ray output, to a disadvantage. Furthermore, in the X-ray radiography control, the time taken for controlling the generation of X-rays is short when compared with a time taken for frame reading of the television camera, involving thus another problem. Additionally, control algorithm for ensuring proper brightness for the fluoroscopic image as well as the radiographic image of a concerned part as required for diagnosis is not definite, bringing about a further problem.
An object of the present invention is to provide an X-ray control method and an X-ray apparatus which make it possible to perform the X-ray fluoroscopy/radiography control more pertinently or properly when compared with the conventional techniques in the X-ray fluoroscopy/radiography control in which a video signal is employed.
Another object of the present invention is to provide an X-ray control method and an X-ray apparatus which can ensure enhanced diagnosis performance for inspectors.
For achieving the objects mentioned above, in the X-ray apparatus according to the present invention, a fluoroscopic image in an X-ray fluoroscopy or an X-ray image picked up in a preliminary radiography is used as a reference image for determining a histogram representing a distribution of numbers of data corresponding to image intensities (pixel values) of the reference image. On the other hand, a weighting function having a variable dependent on the image intensities is determined in order to extract properly the image data. In succession, the weighting function and the histogram are multiplied to thereby determine a weighted histogram, and then output power of an X-ray tube is so controlled that a mean value of the weighted histogram assumes a predetermined value.
Describing briefly the effects achieved by typical embodiments of the invention disclosed in the present application, they are as follows:
(1) In the X-ray fluoroscopy/radiography control for which the video signal is made use of, the X-ray fluoroscopy/radiography control can be carried out more properly when compared with the conventional technique.
(2) With the X-ray fluoroscopy/radiography control in which the video signal is made use of, diagnostic performance can be enhanced.
(3) Because the X-ray apparatus can be implemented in a simplified structure, there can be provided an X-ray diagnosis system of low cost.
(4) The X-ray fluoroscopy can be realized in a stabilized manner.
(5) Sensitive reaction of the sensor in response to movement of an object under inspection can be suppressed.